Pump



L.ASPELIN PUMP 4 Sheets-Sheet 1 Filed March 17, 1954 $2. 7 Figs. I

Feb. 2, 1960 L. L. ASPELlN 2,923,245

PUMP

Filed March 17, 1954 4 Sheets-Sheet 2 [ESL/E L. Alana/1v Feb. 2, 1960 L. L. ASPELIN PUMP 4 Sheets-Sheet 3 Filed March 17. 195.4

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5 m a v. 6 NM 4; ,o/ m L 2 W J a 2 2 a W/ Z 2 United States Patent i e 2,923,245 PUMP Leslie L. Aspelin, Cleveland Heights, Ohio, assignor to Tlfiilrmpson Raiiio Wooldridg'e Inc., a corporation of O '0 This invention relates to a pump especially adapted for power steering to deliver the desired flow of hydraulic fluid while being driven by the vehicle engine throughout a wide range of speeds. Specifically, this invention deals with an angular piston and cylinder type pump adapted to be mounted on an automobile generator and encased in a pond of hydraulic fluid to supply this fluid at a substantially constant flow rate to an actuator for power steering or the like, without unduly working the fluid or consuming excess power when driven at speeds in excess of those required for maintaining the-desired flow rate.

Rotary pumps of the type in which a series of angular plungers or pistons are reciprocated in holes or bores of rotatably driven cylinder blocks in angular relation to each other are known in the art. Such pumps generally have the cylinder blocks riding on end faces of the pump casing and have thereby been subject to excessive wear and have presented diflicult sealing problems. It has, therefore, been proposed to balance the thrust loads of the cylinder blocks on the end faces of the pump casing as a function of pressure developed by the pump by bleeding fluid under pressure into the Space between the cylinders and by regulating the relative areas of the inner and outer faces of the cylinders. This technique has satisfactorily maintained a sealing film of fluid between the outer end faces of the cylinder blocks and the end walls of the casing when the inner and outer face areas of the cylinder blocks are carefully and accurately sized but manufacturing tolerance requirements make it diflicult to mass-produce such pumps and to change pump sizes and the number of angular pistons or plungers without a redesign of the relative area sizes.

The present invention now provides for the balancing of the cylinders to deliberately control their axial positions relative to the end faces of the pump casing without regard to the relative area sizes of the inner and outer faces of the cylinder block. The control of this invention is accomplished by directconnecting of the space between the angularly disposed cylinder blocks to the discharge line of the pump and the controlled release of pressure in the space between the cylinders so that the pressure in the space between the cylinders will always be a controlled amount less than the pressure developed by the pump. Since portions of the outer end faces of these cylinders are exposed to the pump inlet pressures, the pressure in the space between the cylinders will always develop a thrust force that is greater than the opposed thrust force delevoped on the outer faces of the cylin- 'Patented Feb. 2, 1960 2 as would ordinarily develop on high speed operation of the pump. These excessive thrust loads will squeeze out the oil film betweenthe cylinder blocks and the casing walls creating excessive wear and unwanted noises.

An important additional feature of this invention resides in the automatic unloading of the pump whenever pressures in excess of a predetermined maximum are developed For this purpose, a spring biased relief or topping valve automatically vents the space between the cylinder blocks to pump inlet pressure thereby permitting the pump discharge pressure on the outside faces of the cylinder blocks to axially shift the blocks toward each other and olf of the end walls of the casing. This unseating of the cylinder blocks joins the inlet and outlet ports of the pump. As a result, the flow rate and discharge pressure of the pump is automatically maintained below a predetermined maximum regardless of the speed of operation of the pump. At the same time, the excess fluid is not being worked and the load on the pump is relieved so that cool operation can be maintained.

It is then an object of this invention to provide a pumpespecially adapted for operation throughout a wide range of speeds to deliver a substantially constant rate of flow under a predetermined maximum pressure without working the fluid whenever the operating speeds of the pump are such to delvelop excessive flow rates or pressures.

A further object of this invention is to provide an automatic unloading control for pumps to directly join. the pump inlet and outlet ports whenever the pump tends to deliver fluid in excess of a predetermined maximurm rate.

A further object of this invention is to provide a con-- trol for pumps of the angular piston and rotary cylinder block types which will regulate the thrust loads of the: cylinder blocks on the end faces of the pump casing regardless of the areas of the end faces of the cylinder blocks so as to eliminate noise and excessive thrust loads.

A still further object of the invention is to provide an automatic control for an angular piston and rotary cylinder type pump which maintains the space between the cylinder blocks of the pump at pressures lower than the pressures developed by the pump and which automatically unloads the pressure between the cylinders A still further object of this invention is to provide a pump adapted to be attached to the generator of an automobile engine for co-rotation therewith and adapted to be cooled by the hydraulic fluid which it pumps.

A still further object of this invention is to provide a submerged generator-driven pump for vehicular power steering.

A specific object of this invention is to provide a pump of the angular piston and rotary cylinder type having axially shiftable cylinder blocks controlled by pump discharge pressure downstream from a fixed orifice and automatically unloaded to directly join its inlet and outlet ports and to decrease its working stroke whenever excessive discharge pressures are developed.

Other and further objects of this invention will be apparent to those skilled in the art from the following detailed description of the annexed sheets of drawings which, by way of preferred embodiment, illustrate several modifications of the invention.

0n the drawings:

Figure 1 is a somewhat diagrammatic eelvational view of a pump of this invention mounted on the generator of an automobile engine for supplying hydraulic'fluid to a power steering apparatus on the vehicle driven by the engine;

Figure 2 is an enlarged cross-sectional view with parts in end elevation, taken substantially along the line II--II of Figure 1;

Figure 3 is a longitudinal cross-sectional "iew, with parts in elevation, taken along the line III-HI of Figure 2.; a r V Figure 4 is a fragmentary longitudinal elevational view, with parts in elevation, taken along the line IV- -IV of Figure 2;

Figure 5 is a somewhat diagrammatic longitudinal cross-sectional view, with parts in elevation, illustrating the operation of the pump of Figures 1 to 4;

Figure 6 is atransverse cross-sectional view, with parts in elevation, taken along the line VIVI of Figure 3;

Figure 7 is a transverse cross-sectional view, with parts in elevation, taken along the line VIIVII of Figure 3;

Figure 8 is a transverse cross-sectional view, with parts in elevation, taken along the line VIII-VIII of Figure 3;

Figure 9 is a somewhat diagrammatic longitudinal cross-sectional view similar to Figure 5 and illustrating the modified control arrangement for the pump;

Figure 10 is a fragmentary longitudinal cross-sectional view of the central portion of the pump of Figs. 1 to 8 showing another manner of venting the space between the pistons to pump discharge pressure; and

Figure 11 is a view similar to Figure 10 but illustrating a further modified control arrangement for the pump.

As shown on the drawings:

The pump 10 is illustrated in Figure 1, as mounted on a generator 11 of an automobile engine 12. This engine 12, as is conventional, has a crankshaft-driven pulley 13 driving a fan belt 14 which belt, in turn, drives the fan pulley 15 for rotating the cooling fan 16 of the engine. A pulley 17 on the generator 11 engages the fan belt 14 to be driven thereby. The generator shaft 18 is joined by a coupling19 to the pump shaft 20.

The pump casing 21 has, as best shown in Figure 3, a large end head 22 at one end thereof and a smaller end head 23 at the other end thereof. The end head 22 has an external V-groove 24 adjacent the outer end face 25 thereof and this end face abuts the end face 26 of the casing of the generator 11. The generator casing also has a V-groove 27 similar to the groove 24' adjacent the end face 26. A pin '28 seated in recessesrespcctively provided in the end faces 25 and 26, controls the radial alignment of the pump casing. on the generator and a clamping ring 29 extending around the grooves 24 and :27 releasably connects the pump on the generator casing with the end face 25 of the pump head 22 abutting the end head 26 of the generator casing.

A drawbolt or'the like 30 (Figure 1) is provided to tighten the ring 29.

The entire pump casing 21 is enclosed in an outer housing 31 of substantially cup-shape with an openend 32 receiving the end head 22 of the pump. A groove 33 in this head 22 carries the seal ring 34 for engaging the inner face of the housing 31 adjacent the open end 32 thereof. Longitudinal fins 35 radiate from the casing 31 around the periphery thereof.

The closed end wall 36 of the casing 31 has bosses 37 and 38 thereon carrying fittings 39 and 40 respectively. The fitting 39 registers with the discharge passage 41 of the pump casing 21 and is located adjacent the top of the housing 31. The fitting 40 communicates with the interior of the housing 31" near the bottom thereof.

As shown in Figure 1, a feed line 42 extends from the fitting 39 to the actuator 43 of a power steering apparatus 44 of any suitable design. Return fluid from the actuator 43 is fed to the fitting 40 through a tube 45. As is conventional, the steering wheel 46 of the vehicle mounted on the steering column 47 controls a valve (not shown) in the power steering apparatus 44 for regulating the admission of fluid to the actuator 43 thereby driving.

the steering pitman arm 48.

Hydraulic fluid is maintained in the housing 31 at level near the top thereof so that the pump casingZ-l will be substantially submerged in the fluid to be cooled thereby. Heat from the fluid is radiated from the casing 31 by the fins 35.

As best shown in Figure 3, the pump casing 21 has a pair of cylindrical bores 49 and 50 extending inwardly from the end heads 22 and 23 in angular relationship. The angle between the bores 49 and 50 is less than 180 and more than preferably about Shoulders 5'1 and 52 are provided at the inner ends of the bores. 7 Cylinder blocks 53 and 54 ride in the bores and are of less axial length than the bores so as to be axially shiftable toward and away from the shoulders 51 and 52 toward and away from each other. A space 55 is thereby provided between the cylinder blocks.

The cylinder blocks can be composed of metal, plastic, or the like material, and are capable of having good bearing relationship with the metal of the casing defining the bores in which they ride.

The cylinders each have longitudinal holes 56 extending therethrough in spaced parallel relation around the axial centers thereof. These holes 56 receive angled hollow pistons or plungers 57, the angled end portions of which are freely slid-able in the holes. The piston knees are disposed in the space 55 between the cylinders.

The shoulders 51 and 52 are adapted to be abutted by the inner end faces 53 and 59 respectively of the cylinders 53 and 54 so that these faces will always be held in spaced apart relationship with their entire areas thereof exposed to the space 55.

The outer end face 60 of the cylinder 53 rides on the end head 23 of the casing while the outer end face 61 of the cylinder 54 rides-on the end head 22 of the casing.

The outer end face 61 of the cylinder 54 is recessed at 62 and the side walls of the recess are splined at 63 to receive the splined end 20a of the drive shaft 20; The end face of the head 22 on which the cylinder 54 rides is provided with a discharge port 64 registering with the pumping spaces of the holes 56 when the pistons 57 are adjacent the outer end faces 60 and 61 of the cylinder blocks to receive fluid therefrom. A passageway 65 in the end head 22 connects the port 64 with the upstream face of an orifice plate 66 seated in the discharge passageway 41 of the casing 21. This plate 66 has an orifice 66a restricting the flow of pump fluid for maintaining a pressure differential between the passageway 65 and the outlet passage 41. A blind inlet port 67a is also provided in the end face of the end head to form the pumping spaces of the holes 56 when the pistons are retracted from the outer end faces of the cylinder blocks. 7

The end head 23 has a main inlet port 67 opposite the blind port 67a registering with the pumping spaces of the holes 56 in those areas where the pistons are retracted from the end faces 60 and 61 of the cylinder blocks. This end head 23 also has a blind outlet port 64a opposite the live port 64. The blind ports 64a and 67a coact with the main ports 64 and 67 respectively so that both ends of the pumping spaces will be simultaneously joined as the holes 56 pass over the port areas.

The inlet port 67 is connected through a passageway 68 in the end head 23 with an inlet opening 69 adjacent the bottom portions of the housing 31 so as to receive hydraulic fluid direct from the housing.

In accordance with this invention, a bleeder passageway 70 directly connects the space 55 between the cylinder blocks 53 and 54 with the discharge passageway 41 downstream from the orifice 66a to feed fluid being discharged by the pump directly to the space 55. This fluid under pressure in the space 55 acts on the faces 58 and 59 of the cylinder blocks 53 and 54 to urge the same outwardly and force the outer faces 60 and 61 thereof against the end heads 23 and 22 respectively.

As best shown in Figures 2, 4 and 5, the pump casing 21- has a bore 71 parallel with the discharge passageway 41-and intersecting the bleeder passageway 70. This here 71 communicates through a passage 72 in the end head 22 with the passage 65 upstream from the orifice plate 66. A solid cylindrical plunger valve 73 slides in the bore 71 at the end thereof adjacent the passage 72 to be acted on by pressure developed by the pump in the passage 65. This valve 73 is urged by a spring 74 in the bore 71 against the end head 22 and when so bottomed on the end head, has the circumferential groove 75 thereof out of registration with a bleeder passageway 76 that joins the space 55 between the cylinder blocks with an outlet passage 77 communicating with the interior of the housing 31. The spring 74 is bottomed on a fixed orifice plate 78 locked in the bore 71 and having an orifice 78a closed by a topping valve or relief valve 79. A spring 80 acts on the valve 79 to seat the nose 79a of the valve in the orifice 78a for closing the orifice. The spring 80 is bottomed by a screwplug 81 closing the end of the bore 70. A bleeder passage 82 vents the downstream giile of the orifice plate 78 with the interior of the housing 'It will be noted that the bleeder passage 70 communicates with the upstream side of the orifice plate 78 and with the front face of the valve 73 so that both the valve 73and the valve 79 are always subjected to the discharge pressure downstream from the orifice plate 66 which pressure tends to assist the spring 74 in holding the valve 73 against the end head 72 with its groove 75 out of registration with the passageway 76 while simultaneously attempting to unseat the relief or topping valve 79 from the orifice 78. This action of the spring 74 and the discharging pressure on the valve 73, however, is opposed by the higher discharge pressure of the pump upstream from the orifice plate 66 and existing in the passageway 65. This latter higher pressure tends to shift the valve 73 against the spring bias 74 for registering the groove 75 with the bleeder passageway 76 and thereby venting the space 55 to the interior of the casing 31 through the passages 76 and 77. This venting of the space 55 to inlet presstre in the housing 31 will lessen the load on the inner faces 58 and 59 of the cylinder blocks whereupon pump discharge pressure acting on the outer faces 60- and 61 of the cylinder blocks, will shift the blocks axially toward the shoulders 51 and '52 of the bores and off of the end faces of the end heads. As shown in Figure 5, passages 83 and 84 are thereby opened up between the end heads and the outer end walls of the cylinder blocks. These passages are effective to conect the outlet port 64 with the inlet port 67 through the holes 56 and the interiors of the pistons 57.

The orifice 66a in the plate 66 is sized for maintaining a predetermined pressure differential on the upstream and downstream sides of the plate and when the pump is speeded up to deliver excessive amounts of fluid to the downstream side of the plate, the valve 73 will be shifted by the increased upstream pressure for venting the space 55 to inlet pressure. This bleeding of the space 55 through the passageways 76 and 77 will be suflicient to partially unload the cylinder blocks so as to eliminate heretofore encountered pump noises caused by excessive loading of the blocks against the end heads. In the event, however, the pump speed is such as to develop excessive back pressures even at low flow rates in the passage 41, then the topping valve 79 will be unseated due to the pressure in the bore 71 exerted through the bleeder passageway 70 on the orifice plate 78. The valve 79 will thereby be opened to directly vent the space 55 and the discharge passage 41 with the interior of the housing 31. In such event, the pump pressure will be relieved and the cylinder blocks 53 and 54 can shift even closer together to increase the passages 83 and 84.

From the above description, it will be understood that the pump of this invention will deliver a substantially constant flow of fluid at less than a predetermined maximum pressure even when the pump is speeded up by the engine '12 to deliver excessive volumes of fluid or to develop excessive pressures. The shifting of the cylinder blocks 53 and 54 not only eliminates heretofore encountered pump noises developed at high speeds in the angular piston type of pump, but also joins the inlet and outlet ports of the pump so that hydraulic fluid is not worked when not needed. At the same time, the pump is adapted to develop the desired flow rate at the desired pressure even when it is driven at very' low speeds because in such event, the full pumping capacity will be utilized. Since the excess fluid is not worked the fluid doe'snot become unduly heated and the pump is not consuming excessive power when the power steering actuator 43 does not call for fluid. At the same time, the fluid is instantly available at the desired pressure when the steering wheel 46 is manipulated to admit fluid to the actuator.

Since the control of the pump is a function of flow and pressure developed "by the pump, wide tolerances can be accommodated and Widely variable pump sizes can be made without changes in the basic pump design. Accurate relative sizing of the inner and outer faces of the cylinder blocks is not necessary as long as the inner faces, when subjected to the throttled discharge pressure downstream from the orifice 66a, develop more thrust than the outer faces of the blocks which are partially vented to inlet pressure.

In the modification diagrammatically illustrated in Figure 9, parts identical with parts described hereinabove, have been marked with the same reference numerals.

In the pump of Figure 9, the space 55 between the cylinder blocks 53 and 54 is vented through a passage 91 with a spring loaded ball check relief valve or topping valve 92 having a ball 93 spring loaded by a spring 94 against a seat 95. The spring is adjustably loaded by a plug 96. The ball 93 selectively vents the passage 91 with an outlet passage 97 communicating with the pump inlet.

The outlet passage 41 of the pump slidably receives a thimble-type flow valve 98 which is spring biased by a springf99 to cover a vent 100 communicating with the pump inlet. The valve 98 has a fixed orifice 98a in the head end thereof and is adapted to maintain a pressure differential between the upstream and downstream sides of the valve. When this pressure differential increases the valve will be shifted against the spring bias to open the vent 100 whereupon the excess pressure will berelieved.

The outlet passage 65 of the pump is also connected through a passage 101 with the space 55 between the cylinder blocks. This passage 101 contains a fixed orifice vplate 102 for maintaining a predetermined differential on opposite sides of the plate.

In operation, the pump 90 will develop the desired flow rate at the desired pressure at relatively low speeds. When the flow rate increases to increase the pressure differential across the valve 98, the valve will be shifted to relieve the excess flow. When an excessive pressure is developed by the pump in the passageway 41 so as to increase the pressure difierential across the fixed orifice plate 102, pressure in the space 55 will be increased eventually to a point where the ball 93 will be unseated to vent the space 55 and permit the cylinders 53 and 54 to move toward each other thereby relieving the thrust load on the cylinders and connecting the inlet and outlet ports of the pump.

The arrangement of Figure 9 is such that the topping valve. 93 will automatically open to decrease the pressure developed by the pump whenever. the pressure exceeds a predetermined amount while the flow valve 98 will maintain a constant flow delivery rate for the pump by selectively connecting the pump outlet with the pump inlet through the vent 100.

half the discharge pressures developed by the pump since some of the pistons will be vented to the inlet port and others will be at the same time connected to the outlet port. This pressure in the space 55 will be controlled as in the pump 10, through the passage 76 to the valve 73 (shown in Figs, 4 and 5) and the valve will operate to relieve excess pressures for permitting the cylinder blocks to ride oif of their end face seats.

In the simplified pump 110 of Figure 11, the pressure in the space 55 between the cylinder blocks 53 and 54, is developed by connecting the space to the pump discharge pressure through a passage 111 containing a fixed orifice plate 112. This space 55 is also vented to pump inlet pressure through a passageway 113 containing a fixed orifice plate 114. The sizes of the orifices in plates 112 and 114 are selected to maintain, a predetermined pressure in the space 55 relative to the outlet pressure of the pump and thereby balance the axial thrust loads on the cylinder blocks. These orifice plates 112and 114 will always maintain a pressure in the space 55 which is less than the pump discharge pressure but which will increase as pump discharge pressure increases thereby holding the cylinder blocks against the end faces of the end heads 22 and 23 with a variable thrust designed to prevent substantial leakage without excessively loading the blocks at low pump pressures. If desired, of course, the space 55 can also be vented by means of a topping valve or relief valve as in the embodiment shown in Figure 9. The orifice plates 112 and 114 provide a simple expedient for balancing the pump so as to maintain a desired thrust on the cylinder blocks which will eliminate noise even at high speed operation.

It will be understood that many variations of the'illustrated methods of balancing the cylinder blocks in accordance with the flow rate developed by the pump are possible and are within the scope of this invention. This balancing eliminates heretofore encountered pump noises and excessive wear on the pump cylinder blocks. The feature of deliberately leaking the pump fluid across the end sealing faces of the pump to join the inlet and outlet ports' of the pump for silencing the pump and for preventing useless working of fluid that is not required for operation, is a very important one and makes possible maintenance of cool actuating fluid for power steering apparatus, refrigerators, air conditioners, and the like, while continuously operating the pump throughout a wide range of speeds and pressures.

It will be understood that variations and modifications may be efiected without departing from the scope of the novel concepts of this invention.

I claim as my invention:

1. In an angular piston pump of the type having cylinder blocks rotatablymounted and axially shiftable in angularly displaced adjacent bores and hollow angled pis tons slidably mounted in holes of the cylinder blocks and connecting said blocks for co-rotation, the improvement of holes extending through the walls of said hollow pistons communicating between the interiors of the pistons and the space between the cylinder blocks whereby said space will be subjected to the mean pressure of the piston interiors for urging the cylinder blocks outwardly in their bores.

2. A pump adapted, for variable speed driving todeliver a substantially constant flow at a predetermined pressure which comprises a pump casing having a pair of bores in angular relation with a common space therebetween, end heads for said casing closing said bores, cylinder blocks rotatable and axially shiftable in said bores, said cylinder blocks having longitudinally extending holes therethrough, angled hollow pistons having the legs thereof slidably mounted in the holes of both cylinder blocks and extending across the space between the blocks, an inlet port in one end head communicating with the holes in the cylinder blocks to admit fluid thereto, an outlet port in the other end head communicating with the holes in the cylinder blocks to releasepumped fluid therefrom; said pump casing having afixed orifice throttling flow from the outlet port, a passagewayconnecting the discharge from the orifice to the space between the cylinder blocks, an outlet passage in said pump casing communicating with said space between the cylinder blocks, and means controllably releasing pressure from said space through said outlet passage.

3. In a pump of the angular piston and rotary cylinder type having a pumphousing rotatably journaling a pair of spaced cylinder blocks defining a pressure responsive space therebetween, said cylinder blocks riding against end faces of the pump housing to seal the inlet and outlet ports of the pump, the improvements of orifice means throttling flow from the pump, a passageway connecting the downstream side of said orifice means with the space between the cylinder blocks, a relief passageway connected to vent said space between the cylinder blocks to a low pressure area in said pump, and valve mea-ns in said relief passageway to control the venting flow there= through.

4. A pump which comprises a casing, an end head on one end of the casing, a cup-shaped housing surrounding said casing and receiving the-end head in the open mouth end thereof, said casing efining a pair of bores in angular relation, one of said bores being closed by said end head, an end head inthe housing closing the other of said bores, opposed cylinder blocks rotatably and slidably mounted in said bores and riding against said end heads, said blocks having spaced axially extending holes therethrough, hollow angular pistons having the end legs thereofslidably mounted in holes of both blocks, the end head in said housing having an inlet for supplying fluid from the housing to the holes and pistons, the end head in the mouth of the housing having an outlet port receiving fluid-fromsaid holes, afixed orifice plate in the casing receiving fluid from the outlet port to create a pressure diiferential on the upstream and downstream sides thereof, means in said casing connecting the space between the cylinder blocksto pump outlet pressure downstream from the orifice plate to urge the cylinder blocks outwardly against the end head by fluid pressure, a relief passage leading from said space, and spring loaded pressure responsive valve means in said relief passage connected to the'downstream side of said orifice plate andventing the space between the cylinder blocks to the interior ofthe housing at a predetermined maximum downstream presure, whereby pressure in the space between the cylinder blocks will be controlled as a function of pump discharge pressure downstream from the orifice andexcess pressure in said space will be relieved to control the loads of the blocks on the endheads and'pump discharge will be reduced withreduction of pressure in said space;

5 .1 In a pump of the angular piston and rotary cylinder block type having the cylinder blocks thereof-urged into sealing engagement with end faces of the pump casing by iluid inthe space between the cylinder blocks, the improvements which comprise throttling meansin the pump outlet reducing the pressure of flow from the pump, a passageway joining the pump outlet downstream from the throttling means with the space between the cylinder blocks, passage means connected to selectively vent the space between the cylinder blocks, and pressure responsive valve means in said passage means connected across said throttling means for opening the passage at a predetermined pressure diiierential for controlling the pressure in said space as a function of the discharge flow rate of the pump.

6.; In'a pump of the angular piston and rotary cylinder block type having a pair of axially shiftable cylinder blocks seatable against end walls of the pump casing under the influence of pressure in the space between the cylinder blocks and having an intake conduit and a discharge conduit, the improvement which comprises a. bleecler passageway connected to said space and to said discharge conduit to develop thrust forces on the inner faces of the cylinder blocks for urging the blocks apart and against the end walls, passage means connected to said space for relieving fluid from said space, and a pressure responsive flow control valve means in said passage means connected to the discharge conduit and responsive to said pump discharge pressure and opening said passage means in response to a predetermined pump discharge pressure for relieving the pressure in said space and controlling pump output as a function of pump discharge pressure.

7. -In a pump of the angular piston and rotary cylinder block type wherein the cylinder blocks are urged against end heads by pressurized fluid between the blocks for separating the pump inlet and outlet, the improvement of orifice means throttling the outlet flow from said pump, a control plunger having opposed ends slidably mounted in a bore in said pump and respectively connected to pressures on the upstream and downstream sides of said orifice means, a fluid pressure source connected to the space between the cylinder blocks for pressurizing said space, a relief passageway connected to the space between the cylinder blocks, and valve means interposed in said relief passageway and controlled by the position of said control plunger for controlling flow through said passageway whereby pressure in said space will be relieved whenever the pressure differential on opposite sides of the orifice exceeds a predetermined differential.

8. In combination, an angular piston pump having cylinder blocks rotatably mounted in angular relation and axially shiftable toward and away from each other with a pressure space therebetween, hollow angular pistons connecting the blocks and slidable in holes in the blocks, means defining bores in angular relation containing the cylinder blocks, means defining a plurality of inlet and outlet ports in the ends of the bores whereby movement of the blocks away from the ends of the bores will permit leakage across the ends of the blocks to reduce the pump output, a discharge conduit leading from the pump, a fluid pressure source connected to said pressure space for directing fluid pressure into said space, a pressure relief passage leading from said space, valve means interposed in said relief passage, and valve control means operatively connected to said valve means and to said discharge conduit and responsive to flow rate through said discharge conduit to operate said valve means and relieve pressure in said space at a predetermined maximum flow rate whereby a uniform pump output flow rate is maintained.

9. In combination, an angular piston pump having cylinder blocks rotatably mounted in angular relation and axially shiftable toward and away from each other with a pressure space therebetween, hollow angular pistons connecting the blocks and slidable in holes in the blocks, means defining bores in angular relation containing the cylinder blocks, means defining a plurality of inlet and outlet ports in the ends of the bores, whereby movement of the blocks away from the ends of the bores will permit leakage across the ends of the blocks to reduce the pump output, a discharge conduit leading from the pump, a fluid pressure source connected to said pressure space for directing a fluid pressure into said space, a pressure relief passage leading from said space, valve means interposed in said relief passage controlling flow through said relief passage, and valve control means connected to said discharge conduit and responsive to discharge rate and pressure and operatively connected to said valve means opening said valve means at a predetermined maximum pressure and a predetermined minimum flow rate to control pump discharge.

10. In an angular piston pump of the type having cylinder blocks rotatably mounted in angular relation and axially shiftable toward and away from each other together with hollow pistons connecting the blocks and slidable in holes of the blocks, and having an inlet conduit and a discharge conduit, the improvement of a first flow restricting passageway connected to the pump discharge conduit and communicating with the space between the cylinder blocks, and a second flow restricting passageway communicatingwith the space between the cylinder blocks for venting said space, said flow restricting passageways having sizes to maintain a pressure in said space between the cylinder blocks less than the pressure in said pump discharge conduit and a function of said discharge pressure.

11. In combination, an angular piston pump having cylinder blocks rotatably mounted in angular relation and axially shiftable toward and away from each other with a pressure space therebetween, hollow angular pistons connecting the blocks and slidable in holes in the blocks, means defining bores in angular relation containing the cylinder blocks, means defining a plurality of inlet and outlet ports in the ends of the bores whereby movement of the blocks away from the ends of the bores will permit leakage across the ends of the blocks to reduce the pump output, a discharge conduit leading from the pump, an orifice in said discharge conduit, a pressurizing conduit connecting said pressure space with said discharge conduit, a pressure relief conduit leading from said pressure space, a pressure relief valve plunger, a chamber slidably housing said pressure relief valve plunger and having a head end and a rear end with said valve plunger moving toward said head end to a closed position and moving toward said rear end to an open position, flow ports connected to said pressure relief conduit and positioned to be open to relieve said conduit in said open position of said pressure relief plunger, passage means connecting the head end of said chamber upstream of said orifice and connecting said rear end of said chamber downstream of said orifice, spring means urging the plunger toward the head end of said chamber so that said spring means will be overcome at high pump speeds and increased pump discharge pressure upstream of said orifice to partially unload said pressure space and said blocks, and a spring loaded pressure responsive topping valve connected to the discharge conduit downstream of said orifice and responsive to discharge conduit pressure and connected to said pressure space to open at a predetermined maximum pressure in said discharge conduit and vent said pressure space.

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